Gas burner having a diffuser for mixing combustion air and gas

ABSTRACT

Gas is mixed with air with the aid of a diffuser and is drawn into a hollow core of a radiant burner. The diffuser has a plurality of spring fingers around the top of a gas outlet orifice. The fingers carry a shallow cup having a concave surface which faces the orifice and deflects gas laterally and rearwardly in a mixing chamber surrounding the diffuser. Incoming air is thoroughly mixed with the gas in the mixing chamber prior to the induction of the mixture into the hollow core. Gas is burned on the surface of the radiant burner and the products of the combustion heat air for, for example, room heating.

United States Patent [1 1 Teague, Jr.

1 Nov. 13, 1973 [22] Filed:

[ GAS BURNER HAVING A DIFFUSER FOR MIXING COMBUSTION AIR AND GAS [75]Inventor: Walter D. Teague, Jr., Nyack, NY.

[73 Assignee: Southern California Gas Co., Los

Aussie alif: 1.

Aug. 21, 1972 211 Appl. No.: 282,287

Related U.S. Application Data [62] Division of Ser. No. 65,374, Aug. 20,1970, Pat. No.

[52] U.S. Cl. 431/328, 126/92 C, 431/354 [51] Int. Cl. F23d 13/12 [58]Field of Search 431/326, 329, 354; 239/432 [56] References Cited UNITEDSTATES PATENTS 3,208,247 9/1965 Weil et a1. 431/328 1,223,308 4/1917Bone et al 431/328 2,533,104 12/1950 Golden et a1. 431/328 w 3,506,1984/1970 Van Der Zwaal 431/354 FOREIGN PATENTS OR APPLICATIONS 11,0410/1905 Great Britain 239/432 Primary ExaminerCarrol1 B. Dority, Jr.AttorneyRobert L. Parker et a1.

[57] ABSTRACT Gas is mixed with air with the aid of a diffuser and isdrawn into a hollow core of a radiant burner. The diffuser has aplurality of spring fingers around the top of a gas outlet orifice. Thefingers carry a shallow cup having a concave surface which faces theorifice and deflects gas laterally and rearwardly in a mixing chambersurrounding the diffuser. Incoming air is thoroughly mixed with the gasin the mixing chamber prior to the induction of the mixture into thehollow core. Gas is burned on the surface of the radiant burner and theproducts of the combustion heat air for, for example, room heating.

3 Claims, 7 Drawing Figures PATENTEDNUV 13 1975 SHEELQCF GAS BURNERHAVING A DIFFUSER FOR MIXING COMBUSTION AIR AND GAS CROSS REFERENCE TORELATED APPLICATIONS The present application is a division of US. Pat.application Ser. No. 65,374 filed Aug. 20, 1970 and now US. Pat. No.3,696,802.

BACKGROUND OF THE'INVENTION The present invention relates to gas burnersin general, and in particular to an improved diffuser for mixing gaswith combustion air in a short distance.-

In many situations it is desirable to heat a space without installing acentral heating system. Thus, for example, in small apartments or thelike, particularly in relatively warm parts of the country, it may bedesirable to have separate heating systems for each unit. Similarly, ina mobile home one or more small heaters may be employed. Small heatersmay also be used as auxiliary heating in spaces not adequately heated bya central system. In any of such systems for heating a limited space itis desirable to have complete safety for the occupants of the space,high fuel efficiency, low cost, as small a heater as possible, anattractive heater, and as little intrusion of the heater into the heatedspace as possible.

Individual room space heaters have in the past often involved aplurality of heated exhaust tubes arranged in a wall panel with much ofthe heating being due to natural convection and radiation. Forced airunits for individual rooms have been bulky and relatively impracticalfor most applications. Most such forced air units have been mountedcompletely within a space to be heated and therefore draw combustion airfrom within the space.

One of the problems with gas heaters which adds to their bulk andoverall size is that a great length must be provided for gas toadequately mix with combustion air.

It is therefore desirable to provide a small, low cost, efficient spaceheater for individual rooms or other limited areas. Such a unit shouldbe attractive and preferably occupy only a small amount ,of wall space.

SUMMARY OF THE INVENTION The present invention provides for use ina gasheater or the like a diffuser which materially shortens the spacerequired to effect adequate mixing of combustion air with gas. Thediffuser is mounted immediately in front of the outlet of a gas orificeand has a concave surface facing the orifice. The concave surface is ona member supported, preferably, by a plurality of fingers extending froma fitting which defines the orifice. Combustion air is mixed with gasforced laterally and rearwardly of the concave member into a mixingchamber disposed concentrically about the diffuser and the orifice. Themixed combustion air and gas are drawn into burner where the gas isburned. The products of combustion from the gas and air can be used toheat air which is forced into a space to be heated. 1

These and other features, aspects and advantages of the presentinvention will become more apparent from the following description,appended claims and drawmgs.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 illustrates schematically theflow of gases within a space heater constructed according to principlesof this invention;

FIG. 2 illustrates in longitudinal cross section a gas heater embodyingprinciples of this invention;

FIG. Sis a transverse cross section of the heater of FIG. 2;

FIG. 4 is another transverse cross section of the heater of FIG. 2;

FIG. 5 is a detail of an igniter for the heater of FIG.

FIG. 6 is a longitudinal cross section of a portion of anotherembodiment of space heater; and

FIG. 7 is a transverse cross section of the heater of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT A better appreciation of thenature, effect and purpose of the gas burner of the present inventioncan be had by considering initially the preferred gas heater used withthe burner.

FIG. 1 illustrates schematically the flow of exhaust gases and heatedair in a gas fired space heater constructed according to principles ofthis invention. As illustrated in this schematic drawing, the flow ofcombustion products or exhaust gases is indicated by a series of arrowswithin conduits or passages of the heater. In general, the flow ofexhaust is approximately parallel to the plane of the paper in FIG. 1.Likewise the flow of air in the space heater is indicated by tips andtails of arrows since the flow of air is, in general, substantiallynormal to the plane of the paper. Air flowing out of the plane of thepaper is indicated by an arrow tip in the form of a circle andconcentric dot. Air flow into the plane of the paper is indicated by thetail of an arrow in the form of a circle with a cross inscribed therein.The structural parts illustrated in this schematic of FIG. I areprobably best understood by additional reference to FIGS. 2 and 4. 1

As illustrated in FIGS. 2, 3, and 4 the space heater tion 12 ispreferably mounted on the exterior of a building. A mounting flange 13is connected to the sheet metal housing 10 for attaching the heater to abuilding wall 14 or the like. Theflange I3 is preferably made adjustablein some conventional manner so that the heater can be mounted on wallsof varying thickness, as may be required in a particular installation.With the heater mounted in such an arrangement the front 11 is withinthe building and the back portion 12 of the heater is in the exteriorenvironment.

The sheet metal housing 10 and other sheet metal portions hereinafterset forth are illustrated in the cross sections of FIGS. 2-4 in the formof heavy lines representative of cross sections of the material. Edgesof parts not in cross section are illustrated by lighter quality linesin these figures. The heavy lines are employed rather than attempting toillustrate the thin metal by conventional cross sections in order toimprove the clarity of the drawings.

The housing 10 is lined with thermal insulation 16 for minimizing heattransfer between air within the housing I and the external environment.The insulation serves the additional important function of deadeningsound and assuring quiet operation of the unit both inside and outsidethe region being heated. The housing serves as the exterior of arecirculation air conduit 18 running from the front 11 to the back 12 ofthe heater. Air from the space to be heated enters the recirculationconduit through louvered openings 17 in the housing.

The interior of the recirculation air conduit 18 is principally definedby a substantially cylindrical sheet of metal 19 which also forms theexterior wall of an exhaust conduit 21. The cylindrical exhaust conduitis approximately concentric with the rectangular recirculation conduit18. The interior of the exhaust conduit 21 is defined by anothersubstantially cylindrical sheet metal body 22, substantially concentricwith the sheet metal body 19. The sheet metal body 22 continuesforwardly of the cylindrical portion defining the inside wall of theexhaust conduit into a gooseneck or double elbow portion 23 leading to aheated air port 24, at the lower front of the heater, and within thespace to be heated. Preferably the heated air port 24 is wider than itis high, in order to minimize flow restriction. Thus the sheet metalbody 22 not only defines the interior wall of the exhaust conduit 21,but also forms the exterior wall of a heated air conduit 26, leadingfrom the back 12 of the heater to the front 11.

Substantially concentric with the cylindrical portion of the body 22 isa cylindrical sheet metal member 27 with a closed forward end 28defining a combustion chamber 29 therein. Mounted in and concentric withthe combustion chambers 29 is a porous refractory radiant heater orburner 31, heating of which is described in greater detail hereinafter.Broadly speaking, the exterior of the radiant burner 31 is heated toincandescence by burning gas and emits combustion products from itsentire exterior surface. Since the radiant burner 31 is at incandescenceit serves to rapidly trans fer heat by radiation to the wall 27 of thecombustion chamber 29.

An exhaust passage 32in the form of a rectangular opening relativelylong parallel to the front to back axis of the heater and relativelyshort transverse thereto interconnects the interior of the combustionchamber 29 and the exhaust conduit 21 near the top portion of theheater. An exhaust port 33 at the lower portion of the heater in theform of a short passage relatively short in the direction parallel tothe axis of the heater and relatively long transverse thereto,interconnects the interior of the cylindrical exhaust conduit 21 and theexternal environment outside the heater housing 10.

A conventional fan 34 at the back portion of the heater has its suctionside in fluid communication with the recirculation conduit 18 and itspressure side in fluid communication with the heated air conduit 26.

Referring again to FIG. 1 combustion products emitted from the surfaceof the radiant burner 31 enter the combustion chamber 29 and, along withradiant heat from the radiant burner, heat the surrounding wall 27. Thecombustion products or exhaust, as indicated by the arrows, passupwardly through the exhaust passage 32 and enters the cylindricalexhaust conduit 21 where the flow path divides. The combustion productsthen pass along a generally semi-cylindrical path down each side fromthe top of the heater through the exhaust conduit 21 to the exhaust port33 where they are discharged from the heater. As the exhaust passesthrough the exhaust conduit 21 the walls 19 and 22 thereof are heated.

Air from the space to be heated enters the front of the recirculationconduit 18 through the openings 17 (FIG. 2) and passes to the back ofthe heater through the recirculation conduit. While so passing therelatively cool air is in thermal contact with the wall 19 which isheated by the exhaust, so that preheating of the air occurs. The air isthen passed by the fan 34 (FIG. 2) into the heated air conduit 26through which it flows forwardly in the heater ultimately to bedischarged into the heated space through the heated air port 24. As theair passes forwardly through the heated air conduit it is in heattransfer relation with the wall 22 of the exhaust conduit and the wall27 of the combustion chamber so as to be heated thereby.

It will be seen that the air flows substantially concentrically with theexhaust products from the radiant burner and also the flow of air andexhaust products are approximately counter-current for optimumefficiency. Thus the initially cooler air in the recirculation conduit18 is in heat transfer related with the cooler exhaust in the exhaustconduit 21 and the relatively warmer air in the heated air conduit 26 isin thermal contact with the appreciably hotter exhaust and radiant heatfrom the combustion chamber 29. Such counter-current flow assures aminimum temperature in the exhaust emitted from the space heater and amaximum temperature in the air put into the room being heated. Both ofthese are indicative of optimum efficiency of operation of the spaceheater. Tests indicate an exhaust temperature in the range of 300 to 400F and a thermal efficiency in the order of about percent.

In addition to the air recirculated from the heated space through theheater a selected fraction of makeup air is provided by a make-up airaperture 36 in the back portion of the housing 10 so as to be in fluidcommunication with the'exterior environment. This makeup air aperture ison the suction side of the fan 34 and a portion of the air passingthrough the heater is therefore drawn in through the aperture. Byadjusting the size of the aperture 36 any desired fraction of make-upair can be provided in a heater. Typically 10 percent make-up air isprovided through a 1 /4 inch diameter hole.

It may be noted that the exhaust port 33 and make-up air aperture 36 areboth located on the lower side of the space heater. This arrangement ispreferred so that these openings are inherently protected from theelements. It will be apparent of course that such openings can beprovided one top, side, or back of the heater as may be desired withsuitable baffles or shields to pre- ,vent rain and the like fromentering the interior of the heater. Although both the exhaust port andthe makeup air aperture are located on the bottom side of the heater, noproblem has been found with short circuiting of exhaust products intothe heater when these openings are located about 6 inches apart. If itis desired to locate these openings in some other position it will beapparent that suitable baffles can be provided to prevent shortcircuiting of combustion products.

The space heater is fueled with natural gas or the like which issupplied thereto through a pipe 37 which is preferably located in a wall14 in which the heater is mounted. The gas line 37 leads to aconventional automatic control 38 typically in the form of anelectrically controlled valve actuated by a conventional temperaa mixingchamber casting 42. The passage 41 termi-' nates in an orifice tip 43having a central circular orifice (not shown) having a size commensuratewith the required gas flow in the space heater. The orifice tip 43 isaligned with and pointed towards the radiant burner 31.

The radiant burner is a conventional commercially available element inthe form of a hollow cylinder or porous refractory material, open at oneend and closed at the opposite end. The porosity of the refractorymaterial is selected so that during normal operation the flow rate of acombustible gas-air mixture through the pores is greater than the flamepropagation rate. Prior to passing through the walls of the radiantburner 31 the combustion gas is mixed with combustion air and combustionoccurs in a thin region adjacent the outside surface of the radiantburner. The combustion in this region heats the external surface of theradiant burner, which because of its rough porous surface has a highemissivity, to incandescent temperatures. The flow of gas air mixturefrom the interior of the radiant burner towards its outside surfacemaintains the interior relatively cool and substantially below theignition temperature. Because the gas must pass through the porousrefractory body of the radiant burner there is a pressure drop acrossthe wall, and the interior of the radiant burner is pressurized somewhatrelative to the exterior by an amount dependent on flow rate andporosity.

Combustion occurs over substantially the entire outside surface of theradiant burner (actually a very short distance below the surface) sothat the entire surface is incandescent and radiates to the walls 27 and28 of the combustion chamber 29. The pressure drop across the radiantburner assures that the exhaust products are emitted from the externalsurface of the radiant burner and enter the combustion chamber 29 forflowing through the exhaust system of the space heater as hereinabovedescribed.

A problem that has been faced with previous radiant burners has beenadequatemixing of the fuel gas with combustion air. Unless'the gas andair are thoroughly mixed prior to entering the elongated cylindricalradiant burner, composition gradients may occur, and-nonuniform heatingwith consequentinefficiency and even danger to the burner hasoccured. Avariety of orifice designs have been explored in order to achieveadequate mixing, however, no acceptable arrangement has been provided.In general, it has been necessary to space the gas inlet orifice awayfrom the open mouth forrnly mixed with incoming air prior to enteringthe mouth of the radiant burner 31.

The mixing chamber casting 42 not only includes a substantiallycylindrical central mixing chamber 45 and a gas passage 41 leadingthereto, it also includes a plurality of substantially radiallyextending fins 47. The fins 47 extend outwardly from a pointapproximately in line with the outside wall 27 of the combustion chamberto a point in line with the exterior wall 22 of the heated air conduit.The heated air conduit also includes a substantially conical portion 48enlarging from the cylindrical wall 22 to approximately the effectivediameter of the fan 34. The fins 47 are mounted within this cone 48. Asseen in FIG. 3, the fins do not extend parallel to the axis of theheater, but generally follow a slightly helical path so that airimpinging on the fins of the radiant burner by a distance of about fivediameters. Such a distance is undesirable in a small space heater sinceit unduly lengthens the device and makes it less attractive.

A surprisingly-simple and efficacious solution to the gas-air mixingproblem has been' discovered. In accordance with this discovery, aplurality of spring fingers 44 are provided around the orifice tip 43.The fingers 44 may be formed integral with the mixing chamber casting 42or preferably are attached by the tip 43.

Clipped into the fingers 44 is a shallow cup 46 having its concavesurface facing the gas orifice. The concave inside surface of the'cup 46deflects the gas flow from the orifice and redirects it laterally andrearwardly in the mixing chamber wherein it 'is thoroughly and unifromthe fan 34 is straightened out so as to flow through the heated airconduit 26 parallel to the axis. This is done because the air coming outof the fan 34 is whirling to some extent due to the action of the fanblades and the slightly helical fins counteract this whirling to a largeextent. If desired, radially extending fins can be provided on theexterior wall of the combustion chamber 29 in the heated air conduit tofurther assure axial flow of the air and also to conduct heat from thehot combustion chamber wall 27 to an increased area for thermal contactwith the air. A particularly suitable arrangement is to provide theexterior wall 27 of the combustion chamber in the form of a corrugatedcylinder with the greatest extent of the corrugations running parallelto the axis. This serves to direct the air to some extent and alsosubstantially increases the heat transfer surface area withoutsubstantial cost increase.

In the embodiment illustrated herein an air duct 94 (FIGS. 2 and 3)extends from the pressure side of the fan 34 into the upper portion ofthe mixing chamber 45 for bringing combustion air in for mixing with thegas. The air duct 94 is like a curved scoop between a pair of the fins47 leading forwardly and downwardly to the mixing chamber. A plateconnected to the casting 42 blocks a portion of the inlet to the duct 94and by selecting the size of plate, a desired pressure can be achievedin the mixing chamber and radiant burner for optimum'heater operation.

The arrangement illustrated herein comprises what is known as anonsealed unit since combustion air is 'extracted from a portion of theair stream being heated. The exhaust side of the combustion chamber isof course sealed from the heated air. There is no problem with depletionof the air in the space being heated by such a non-sealed unit since themake-up air aperture 36 is sufficiently large to provide a greaterquantity of make-up air than is required for combustion purposes. Ifdesired a plurality of make-up air apertures can be provided in case ofinadvertent blocking of one of the apertures.

A non-sealed unit as hereinabove described, has an overall length ofabout 20 inches and the portion extending outside the building isapproximately 9 inches square. Within the building, the unit occupies awall space of about 10 by 12 inches, or slightly less. A sealed unit ashereinafter described has the same dimensions, except it is about threeinches longer to provide room for an additional fan.

In order tostart the gas heater in operation when an on signal comesfrom a thermostat power is first applied to a conventional glow ignitersuch as illustrated in FIGS. 4 and 5. The glow igniter comprises aninsulating terminal block 51 mounted in an enlargement of the upperexterior wall 19 of the exhaust conduit 21. Clips 52 conduct current toa resistive element 53 that is rapidly heated to a temperature above theignition temperature of a gas-air mixture. When the igniter 53 reachestemperature the fan 34 is turned on and a short time later the solenoidcontrol valve 38 is opened to admit gas into the mixing chamber 45. Thegas mixes with the air, flows through the porous radiant burner 31,quickly filling the small volume of the combustion chamber and theexhaust passage 32. This brings the gas-air mixture in contact with thehot igniter and the resultant flame quickly propagates back to thesurface of the radiant burner. It is found that ignition occurs in lessthan 1/6 second in such a system and there is no noticeable popping uponignition. It will be apparent to one skilled in the art that otherignition systems such as for example, pilot lights, spark igniters, orthe like can be employed if desired. It is preferred that the igniter belocated at the upper portion of the exhaust conduit so that the gas-airmixture reaches it in a minimum time.

FIGS. 6 and 7 illustrate in side cutaway and rear section, respectively,a gas-fired space heater constructed according to principles of thisinvention in the form of a sealed unit wherein the combustion air supplyis completely independent of the air being heated. Only the rear portionof the space heater is illustrated for showing the air supply since theheating portion, exhaust ducts, radiant burner and the like aresubstantially identical to the non-sealed unit hereinabove described andillustrated.

The sealed unit comprises a sheet metal housing 56, the sides and rearend of which are slightly bulged for decorative purposes to avoid a boxylook on that portion of the unit exterior to the space being heated.Mounted witin the housing 56 is a heated air conduit 57 through whichair is forced by a fan 58. Air enters the suction side of the fan 58through a recirculation conduit 59 within the housing. Within the heatedair conduit 57 is a combustion chamber 61 within which a radiant burner(not shown) is mounted. The combustion chamber, air flow conduits, andexhaust conduits (not shown) are substantially identical to thosehereinabove described and illustrated in relation to FIGS. 1 through 4.

The fan 58 is driven by a conventional electric motor 62, the shaft 63of which is connected to the fan 58 and also to a conventionalcentrifugal blower 64. The suction side of the blower 64 has a centralaperture 65 open to a combustion air plenum 66 formed between a portionof the housing 56 and a sheet metal bracket plate 67, which also servesto mount the blower. The

combustion air plenum 66 is in fluid communication with the exteriorenvironment surrounding the heater through a hole or holes 68,preferably located along the bottom edge of the heater for protectionfrom the elements. A short tube 69 interconnects the blower 64 and motor62, and provides a barrier to prevent air from the heated air system andthe combustion air system from commingling, thereby providing a sealedunit wherein the exhaust products are isolated from the heated air andthe combustion air is not drawn from the space to be heated.

The outlet of the centrifugal blower 64 is connected to an upwardlyextending air flow tube 71 by a rubber sleeve 72. Air passing from thetube 71 flows through a rectangular combustion air conduit 73 runningdiagonally forward along the upper portion of the space heater. Air fromthe combustion air conduit then passes downwardly through a passage 74into the combustion chamber 61 where it enters the radiant burner (notshown) as in the other embodiment.

Inserted through the side of the air tube 71 is a smaller diameter gaspipe 76 ending in an orifice tip 77 within the air tube. Combustion gasis added to the air through the orifice tip 77, and because of the longflow path between the tip and the combustion chamber, thorough mixingwith the combustion air is obtained without use of the deflector cuphereinabove described and illustrated in relation to the embodiment ofFIGS.

Although limited embodiments of space heaters constructed according toprinciples of this invention have been described and illustrated herein,many modifications and variations will be apparent to one skilled in theart. Thus, for example, although the heater has been illustrated withthe exhaust flowing upwardly in the exhaust conduit and downwardly tothe exhaust port, the flow can be from one side to the other, or frombottom to top, as may be desired. As another variation, the externalhousing forming the outer wall of the recirculation conduit can becylindrical for a smaller apparent size and decorative effect. Manyother modifications and variations will be apparent to one skilled inthe art and it is therefore to be understood that within the scope ofthe appended claims, the invention may be practiced otherwise than asspecifically described.

What is claimed is:

1. An improved burner combination comprising:

a. means defining a chamber for mixing air and gas;

b. means defining a gas inlet orifice into the mixing chamber; V c. aduct for introducing air into the mixing chamber; d. a radiant heatburner in the form of a porous cylinder having an open end, the open endfacing the mixing chamber; and

e. a deflector in front of the gas inlet orifice means having a concaveside facing the orifice.

2. The improved burner combination claimed in claim 1 wherein thedeflector includes a segment of a hollow sphere having its'concave sidefacing the orifice.

3. The improved burner combination claimed in claim 2 including springfingers mounted on the gas inlet orifice means and carrying the hollowspherical segment.

1. An improved burner combination comprising: a. means defining achamber for mixing air and gas; b. means defining a gas inlet orificeinto the mixing chamber; c. a duct for introducing air into the mixingchamber; d. a radiant heat burner in the form of a porous cylinderhaving an open end, the open end facing the mixing chamber; and e. adeflector in front of the gas inlet orifice means having a concave sidefacing the orifice.
 2. The improved burner combination claimed in claim1 wherein the deflector includes a segment of a hollow sphere having itsconcave side facing the orifice.
 3. The improved burner combinationclaimed in claim 2 including spring fingers mounted on the gas inletorifice means and carrying the hollow spherical segment.